1. Field of the Invention
The present invention relates to image forming apparatuses and, more particularly, to an image forming apparatus that is capable of controlling a process time gap between an image forming operation and an image processing operation.
2. Description of the Related Art
In recent years, with progress in computerization of information, image forming apparatuses such as a printer, a facsimile, etc., which are used to output electronic information, have become indispensable devices. High-speed processing is required for image forming apparatuses such as a business-use image forming apparatus in a case where the image forming apparatus performs a large amount of image formation to be output or in a case where the image forming apparatus is shared by a large number of persons. In order to satisfy such a demand for high-speed operation, a method is suggested to attempt improvement in a throughput of an image forming process (for example, refer to Patent Document 1). In this method, an execution timing of a starting process and a stopping process of an image forming mechanism (a print engine) that actually performs the image forming process is optimized so as to improve throughput of the image forming process.
Patent Document 1: Japanese Laid-Open Patent Application No. 2001-177676
In an image forming apparatus disclosed in the above-mentioned Patent Document 1, when performing an image forming process by a monochrome print engine, a query is sent to a controller, which performs image processing, to determine whether an object of the print job subsequently supplied is a monochrome image or a color image. If the object of the print job is a monochrome image, the image processing is continued. On the other hand, if the object of the print job subsequently supplied is a color image, a print engine for color images is activated beforehand. Thereby, a time lag caused by a starting process of the print engine is eliminated when performing the subsequently supplied color image print job. Additionally, when performing the image forming process by the color image print engine, a query is sent to the controller for performing the image processing as to whether the object of the print job subsequently supplied is a monochrome image or a color image. If the object of the print job is a monochrome image, the operation of the color image print engine is stopped immediately after the print job is ended to save energy.
However, as an operation cycle of an image forming apparatus, it is typical to perform an image forming process by a print engine after performing image processing by a controller. In order to provide a function to send a query about contents of a print job from the print engine to a controller, a design change is required to a program for controlling the apparatus or a structure of the apparatus. However, providing such a function is not easy. Additionally, if the print engine sends a query about the job contents to the controller and the controller sends a reply about the job contents to the print engine, a communication load is naturally increased. However, it is not desirable to increase the communication load between the controller and the print engine since image data is being sent from the controller to the print engine.
In the meantime, many multi-function image forming apparatuses, such as a copy machine, a printer, or a multi-function peripheral (MFP) having a plurality of image forming functions, are provided with a function to operate parts and units necessary for a job being performed so as to eliminate waste energy. On the other hand, such an image forming apparatus is capable of concurrently processing a plurality of jobs that use different functions (parts and units) when used by a plurality of host apparatuses connected to a network or when having complex functions. Thus, a frequency of activating a common operation part shared by jobs has become high. Under such circumstances, if operations of the common functions and common parts or units are stopped each time one job is ended and the common parts or units are activated again from the stopped state, a waiting time is increased, which elongates a total process time of each job.
In order to solve such a problem, Patent Document 2 teaches a control technique to cause image formation of a plurality of sheets to be performed continuously while an image forming part is maintained in an activated state so as to achieve a high-speed image forming process and prevent waste operation of an operation part to save energy.
Patent Document 2: Japanese Laid-Open Patent Application No. 2000-35705
An image forming apparatus disclosed in Patent Document 2 is capable of performing monochrome mode and color mode image forming operations on recording media that are sequentially conveyed. In this image forming apparatus, a query is made as to whether the mode setting for a subsequent recording medium is a color mode, a monochrome mode or an unfixed mode so as to control operation (activation and waiting or rest) of a color image forming part and a monochrome image forming part in accordance with the mode setting. According to such a control, both a high throughput and a low operating cost can be achieved. The technique disclosed in Patent Document 2 is to optimize the control of operations (activation and waiting or rest) of the color image forming part and the monochrome image forming part that is performed between recording media in consecutive image forming operations. However, the technique does not include an inactivating operation of the color and monochrome image forming parts.